https://official-ongoing-2.gamindustri.us/manga/One-Piece/0573-004.png
Sengokus own admission is that Whitebeard was holding back the entire war.
https://official-ongoing-2.gamindustri.us/manga/One-Piece/0565-007.png
The plan was to execute Ace once Whitebeard was behind the wall. Its only by Whitebeards luck he happened to be saved by Oars.
https://official-ongoing-2.gamindustri.us/manga/One-Piece/0566-005.png
Notice how they don't try to execute Ace when they think Whitebeard can demolish them.
Ish
https://official-ongoing-2.gamindustri.us/manga/One-Piece/0569-009.png
Or how the next time they attempt to execute him Whitebeard acknowledges to Sengoku how weak he is?
Yes, plot is part of it. But the main reason ace wasn't executed immediately was so Whitebeard wouldn't sink marineford and neg them.
Sengokus own admission is that Whitebeard was holding back the entire war.
https://official-ongoing-2.gamindustri.us/manga/One-Piece/0565-007.png
The plan was to execute Ace once Whitebeard was behind the wall. Its only by Whitebeards luck he happened to be saved by Oars.
https://official-ongoing-2.gamindustri.us/manga/One-Piece/0566-005.png
Notice how they don't try to execute Ace when they think Whitebeard can demolish them.
Ish
https://official-ongoing-2.gamindustri.us/manga/One-Piece/0569-009.png
Or how the next time they attempt to execute him Whitebeard acknowledges to Sengoku how weak he is?
Yes, plot is part of it. But the main reason ace wasn't executed immediately was so Whitebeard wouldn't sink marineford and neg them.